This invention relates to the construction or forming of a sheet metal or aluminum can end having a peripheral rim or crown which is double-seamed to the upper edge portion of a sheet metal or aluminum can body. Such a can end is formed from a drawn sheet metal can shell, for example, a shell produced by tooling as disclosed in U.S. Pat. No. 5,857,374 which issued to applicant. Commonly, the formed can shell includes a circular center panel which extends to a panel wall which forms the inner wall of a reinforcing rib or countersink having a U-shaped cross-sectional configuration, and the countersink is connected by a frusto-conical chuckwall to an annular crown which is formed with a peripheral curl. For beverage containers, the center panel of the shell is commonly provided an E-Z open tab, and after the can body is filled with a beverage, the peripherally curled crown of the shell is double-seamed to the upper end portion of the can body.
When the can body is filled with a carbonated beverage or a beverage which must be pasturized at a high temperature, it is essential for the can end to have a substantial buckle strength to withstand the pressurized beverage, for example, a buckle strength of at least 90 psi. Such resistance to xe2x80x9cbucklexe2x80x9d pressure and xe2x80x9crockxe2x80x9d pressure is described in detail in U.S. Pat. No. 4,448,322. It is also desirable to minimize the weight of sheet metal or aluminum within the can end without reducing the buckle strength. This is accomplished by either reducing the thickness or gage of the flat sheet metal from which the can shell is drawn and formed and/or by reducing the diameter of the circular blank cut from the sheet metal to form the can shell.
There have been many sheet metal shells and can ends constructed or proposed for increasing the buckle strength of the can end and/or reducing the weight of sheet metal within the can end without reducing the buckle strength. For example, U.S. Pat. Nos. 3,843,014, 4,031,837, above-mentioned U.S. Pat. Nos. 4,448,321, 4,790,705, 4,808,052, 5,046,637, 6,065,634, 6,089,072 and 6,102,243 disclose various forms and configurations of can shells and can ends and the various dimensions and configurations which have been proposed or used for increasing the buckle strength of a can end and/or reducing the metal in the can end. Also, published PCT application No. WO 98/34743 discloses a modification of the can shell and can end disclosed in above-mentioned U.S. Pat. No. 6,065,634. In addition to increasing the buckle strength/weight ratio of a can end, it is desirable to form the can shell so that there is minimal modifications required to the extensive tooling existing in the field for adding the E-Z open tabs to the can shells and for double-seaming the can shells to the can bodies. While some of the can shells and can ends disclosed in the above patents provide a portion of the desirable features, none of the patents provide all of the features.
The present invention is directed to an improved and refined sheet metal can end and a method of forming the can end which provides the desirable features and advantages mentioned above, including a significant reduction in the blank diameter for forming a can shell and a significant increase in strength/weight ratio of the resulting can end. A can shell and can end formed in accordance with the invention not only increases the buckle strength of the can end but also minimizes the changes or modifications in the existing tooling for adding E-Z open tabs to the can shells and for double-seaming the can shells to the can bodies.
In accordance with a preferred embodiment of the invention, the can shell and can end are formed with an overall height between the crown and the countersink of less than 0.230 inch, and the countersink has a generally cylindrical outer wall and a curved inner panel wall. The frusto-conical chuckwall extends from the outer wall of the countersink to the inner wall of the crown at an angle between 16xc2x0 and 30xc2x0 and preferably between 25 and 30xc2x0. Preferably, the countersink has a generally flat bottom wall which connects with the countersink outer wall and the curved inner panel wall with corner walls having a radius less than the radial width of the bottom wall. A slightly dome-shaped center panel extends from the curved panel wall and has a top center portion which defines a plane extending substantially through the junction of the inner wall of the crown and the frusto-conical chuckwall.
Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.